The present invention relates to a method for modifying the quality of a liquid foodstuff, and more particularly it relates to a method of modification of the quality of a liquid foodstuff for attaining such effects as amelioration of smell of the liquid foodstuff, deactivation of enzymes in the liquid foodstuff and sterilization thereof. The liquid foodstuff-quality modification method of the present invention is one which utilizes carbon dioxide in a supercritical state, so that this method is highly safe in practice thereof and, further, does not require specific high-temperature heating step or heating step under reduced pressure.
Soy sauce which is one of fermented foodstuffs, is a typical Japanese seasoning which has gained popularity overseas along with dishes of Japanese cuisine in recent years. Soy sauce, however, is disliked in part by Japanese and foreigners because of its peculiar smell. It is, therefore, considered a key factor for elevating the utility and value of soy sauce to remove the peculiar smell (odor) of soy sauce and to enhance its mild aroma.
Sake, which is another fermented foodstuff, is generally produced through the following steps. In the first step, fermented rice is compressed and filtered to obtain shinshu (green sake). In the second step, this obtained green sake is sterilized by heating at 60.degree.-65.degree. C. and stored. In the third step, a number of lots of the stored sake which have been heat-treated are properly blended to determine the sake quality (light or dry, etc.) and the alcohol content is adjusted to standards. In the fourth (final) step, the thus prepared sake is again sterilized by heating and then bottled or packed. Thus, in the production of sake, the heat-treatment is conducted twice, in the second and forth steps in the manufacturing process, to effect deactivation of enzymes and sterilization.
The fresh flavor of green sake is sharply reduced by two heat-treatments in the manufacturing process, so that consumers request fresh sake which has been produced without undergoing any heat-treatment. However, green sake, although fresh in taste and smell, is very changeable in flavor because of its high enzymatic activity. There are marketed some brands of non-heat-treated sake said at low temperature as fresh sake, but such fresh sake is subject to deterioration of quality by the action of certain enzymes such as .alpha.-amylase, protease and carboxy-peptidase, which poses the problem of increased distribution costs to prevent of such qualitative deterioration.
In order to solve the above problem, attempts have been made to remove such enzymes in the green sake by precision filtration or ultra-filtration, but sufficient removal of the enzymes has been impossible with such means. Further, the enzyme removal using a membrane has the problem that the aromatic components of green sake may be dissolved in the membrane during the process and/or that some kinds of taste components of green sake may be removed, thereby losing its relish.
Also, with reference to muddled fruit drinks such as orange juice, etc., it is considered that the cloud of the drink is a decisive factor for the quality of the drink. Deactivation of pectin esterase (PE) is essential for maintaining the stability of this cloud, but since PE is an enzyme stable to heat, usually a heat-treatment under a high-temperature condition (88.degree.-99.degree. C. or 120.degree. C.) is required for deactivation of this enzyme. However, the heat-treatment at such high temperature causes deterioration of freshness and characteristic taste of the drink.
As a result of intensive studies for solving the above problems, it has been found that by contacting carbon dioxide of a supercritical state with a liquid foodstuff in a specific condition, the desired amelioration of smell, deactivation of enzymes and sterilization can be accomplished effectively. On the basis of the finding, the present invention has been attained.